The present invention is directed to an actuation tool for subsea completion system components. More particularly, the invention is directed to an actuation tool which comprises an electrical actuator, such as a motor, for actuating a corresponding mechanism on the subsea completion system component.
Subsea completion systems typically comprise a wellhead housing which is located on the sea floor at the upper end of a well bore, a Christmas tree which is secured to the top of the wellhead housing, and a tubing hanger which is landed in either the wellhead housing or the Christmas tree and which supports a tubing string that extends through the well bore and into the subterranean well. Prior to installing the tubing hanger, a blowout preventer (“BOP”) is usually connected to the top of the wellhead housing or the Christmas tree and a low pressure riser pipe is connected between the BOP and a surface rig. The BOP provides a necessary barrier between the well bore and the environment and allows the riser pipe to be disconnected from the subsea completion system in the event of an emergency.
Numerous subsea completion system components include mechanisms which are actuated by hydraulic pressure that is supplied from the surface rig over an umbilical. One such component is a tubing hanger running tool (“THRT”), which is used to install the tubing hanger in the wellhead housing or the Christmas tree. Prior art THRT's commonly include a cylindrical body and first and second generally tubular locking pistons which are slidably supported on the body. The first locking piston is adapted to engage a first locking device to secure the THRT to the tubing hanger, and the second locking piston is adapted to engage a second locking device to secure the tubing hanger to the wellhead housing or the Christmas tree.
During installation of the tubing hanger, a running string is connected to the top of the THRT, the first locking piston is actuated to secure the THRT to the top of the tubing hanger, and the assembly is lowered to the subsea wellhead through the riser pipe and the BOP. Once the tubing hanger is landed, the second locking piston is actuated to secure the tubing hanger to the wellhead housing or the Christmas tree and, when appropriate, the first locking piston is again actuated to release the THRT from the tubing hanger so that the THRT can be retrieved to the surface rig.
The first and second locking pistons are typically actuated by hydraulic pressure which is communicated to the THRT through an umbilical that extends from the surface rig. The lower end of the umbilical is often terminated in a slick joint which is located at the upper end of the BOP when the tubing hanger is landed in the wellhead housing or the Christmas tree. The slick joint allows the BOP rams to close and seal around the running string or the THRT without interference from the umbilical.
Although the slick joint allows the BOP rams to form an effective seal without interference from the umbilical when the BOP is located subsea, several operators are exploring the possibility of mounting the BOP on the surface rig and connecting the BOP with the subsea completion system using a high pressure riser pipe. This arrangement requires that the THRT umbilical pass through the BOP rams, which may prevent the BOP rams from sealing adequately in the event of an emergency. A possible solution to this problem is to connect the umbilical to a special BOP spanner joint which is located adjacent the surface-mounted BOP. However, this requires that the umbilical be cut to an exact length to properly span the distance between the spanner joint and the subsea wellhead or Christmas tree, and the use of such custom-length umbilicals for each subsea completion system is undesirable. Another solution is to employ composite riser pipe joints which incorporate hydraulic conduits for the THRT. However, these composite joints are time consuming to install and their hydraulic conduits are difficult to fill and flush.